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jdemaris
04-03-2004 14:38:11
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Re: Question for jdemaris in reply to BJ, 04-03-2004 08:05:42
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I guess the answer is, I don't know for sure. I DO know of certain things that WILL cause the rings to break, but there may be other factors besides. The 350 series through the "C" series uses square cut rings. If the piston ring grooves get a little loose, basically anything over .003" side clearance, the rings slap back and forth, cause blowby, and eventually shatter. Also, even with unworn pistons, ether tends to break the top rings. The later engines, as used in the 350Ds and on up through the 400G used a slightly bigger bore and Keystone style rings which are wedge-shaped. As I understand it, gas pressure tightens them, they don't slop around, and are much less prone to breakage. The 450s, starting with the "B" series as I recall, used the Keystone rings and they held up much better than the 350s. Another factor, though, is that 350s are somewhat underpowered and get lugged a lot. I don't know if that directly affects the rings, or just tends to make the pistons and sleeves wear out faster. So, when the 350Ds came out with 179 cubic inches instead of 152, they had Keystone rings and also had a little more torque and horsepower. If you plan to reuse your pistons, make sure the side clearance on the top rings does not exceed .003". If it does, but the skirts seem okay, you can buy and install piston groove repair shims for a somewhere around $3 apiece. Years ago, pistons were routinely "rebuilt" and reused by knurling the skirts and regrooving and installing steel shims. But when the 1960s came, rebuilding became more of a "throw-away" process, and new pistons were cheap. Now, things seem to be turning around again because some new parts are pretty damn expensive. Maybe not so bad for your 350, but wait awhile. I recently priced four pistons and four sleeves (actually a sleeve deck) for my 1010 and was given a price of $1200 !! That convinced me to hone my sleeves, put shims in the pistons, and buy new rings.
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